Charging cable connected all the time but only charge when battery is below a given percentage

So I've mounted my Nexus 7 onto a wall and use it as a sort of info screen / home automatisation device. Now this would require the screen to be on all the time which is why I want it to be connected to a charging cable 24/7.

Is there an app in which I can say that the device should only start charging when the battery level falls below 10%? I don't want it to be charging all the time as this would wear off the battery pretty quickly, I guess.

Thanks for any help.